NBS A 11 ID 2 2 b S 2

7

NATL INST. OF STAND & TECH

PUBLICATIONS^ 84-2925 A111 °7

Prediction of Performance for a

Fire-Tube Boiler With and Without

Turbulators

David A. Didion

Lih Chern

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

Center for Building Technology

Building Equipment Division

Gaithersburg, Maryland 20899

July 1984

Sponsored by:

U.S. Army Facilities

Engineering Support Agencies

Tprhnoiogy Support Division

* Tlvoir, Virginia 22060

100

,U56

04-2925

1984

c. 2

NBSIR 84-2925

PREDICTION OF PERFORMANCE FOR A

FIRE-TUBE BOILER WITH AND WITHOUT

TURBULATORS

NATIONAL BUREAU OF STANDARDS

LIBRARY Crrc. - AJ&

David A. Didion

Lih Chern

U S. DEPARTMENT OF COMMERCE

National Bureau of Standards

Center for Building Technology

Building Equipment Division

Gaithersburg, Maryland 20899

July 1984

Sponsored by:

U.S. Army Facilities

Engineering Support Agencies

Technology Support Division

Fort Belvoir, Virginia 22060

U.S. DEPARTMENT OF COMMERCE, Malcolm Baldrige, Secretary

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director

ABSTRACT

A series of computer rues vere made using DEPAB2 (the boiler simulation

computer program). They include the runs for a fire-tube boiler 'as-is'

(i.e. # without turbulators), with wire-coil type turbulators, and with

twisted-tape type turbulators, respectively. Output from these runs are used

to evaluate the boiler seasonal performance values under the Washington, D.C.

weather conditions. Results show that the turbulator increases the boiler

seasonal efficiency from 2.87 to 6.08%.

Key Words: Boiler performance; boiler simulation; enhanced heat transfer;

fire tube boilers; turbulators.

iii
DISCLAIMER

In view of the presently accepted practice of the bnilding industry in the

United States and the structure of the computer software used in this project,

common U.S. units of measurement have been used in this report. In recognition

of the United States as a signatory to the General Conference of Weights and

Measures, which gave official status to the SI system of units in 1960,

appropriate conversion factors are provided below for the units used in this

report.

Temperature F = 9/5 C + 32

Energy 1 Btu = 1.05506 kilojoules (kj)

IV
ACKNOWLEDGMENTS

Thanks to Dr. Joseph Chi of HCP Systems for his invaluable technical

assistance and review, and to Mr. James Thompson of USAFESA for his administrative guidance. Also thanks to Dr. A. Bergles of Iowa State University for

supplying the required input data on forced convection heat transfer

coefficients.

v
TABLE OF CONTENTS

Page

ABSTRACT . iii

DISCLAIMER iv

ACKNOWLEDGMENTS ....... ..... v LIST OF FIGURES vii

1. INTRODUCTION 1

2. CONTROLLERS 1

3. HEATING LOAD 2

4. RESULTS AND DISCUSSIONS 2

5. CONCLUSIONS ......... 4

6 . REFERENCES ............................. 5

APPENDIX .............. A-l

List of Tables A”2

vi
LIST OF FIGURES

Page

Figure 1. Logic for on/off controller and metering controller . . . . . 6

Figure 2 . Heating load curve ..................... 7

Figure 3

Typical weather at Washington, D.C. during the heating

SeaSOn coocoeeeocoeoocooeeeeoeoeoo

Figure 4. Daily fuel utilization efficiency versus outdoor

temperature, full load at 10*F ............... 8

Figure 5. Daily fuel utilization efficiency versus outdoor

temperature, half load at 10®F ............... 9

Figure 6. Seasonal Efficiency ..................... 10

vii

1 . INTRODUCTION

This report describes an investigation on effects of inserts for the boiler

tabes on the performance of the fire—tube boiler. A series of runs for a

typical fire-tube boiler with and without turbulators were made using DEPAB2

[1] and the effect of turbulators on its performance is evaluated employing

the on/off and fuel/air metering controllers. Also, performance comparisons on

an annual basis are made of the fire-tube boiler with and without turbulators.

2. TYPES OF CONTROLLERS

The on/off controller senses the boiler output temperature. Fuel/air supply

turns on when the boiler temperature drops below a lower preset value, and

turns off when the temperature rises above & higher preset value.

The fuel/air metering controller has a primary feedback element sensing the

boiler temperature. The output signal from the feedback element is combined

with the setpoint signal and processed by the fuel/air flow metering

controller. The resultant actuating signal from the fuel/air automatic controller is used to position the burner control elements to adjust fuel/air

flow in proportion to load. There is usually a minimum firing rate for a

boiler burner, so a boiler with an fuel/air metering controller operates in an

on/off mode when heating load is smaller than the boiler steady-state output

at its minimum firing rate.

Curves of steady-state air and fuel flow rates versus the boiler temperature

are shown in figure 1.
3. HEATING LOAD

The boiler heating load is assumed to be proportional to the temperature

difference of 70°F minus the outdoor air temperature. Two heating load curves

have been used. One is that the boiler is at full load at the design outdoor

temperature of 10°F for Washington, D.C. Another is that the boiler is at

half load at the design outdoor temperature of 10°F. These curves are shown

in figure 2. Figure 3 shows the typical weather at Washington, D.C. during a

heating season.

4. RESULTS AND DISCUSSIONS

Results of runs for a typical boiler for the cases of with and without

tnrbulators are summarized in figures 4 and 5, where the fuel utilization

efficiency values are plotted versus outdoor air temperatures. The seasonal

efficiencies under weather conditions described above are plotted in figure 6.

The amount of reduction in fuel consumption by inserting tabulators into the

last pass of the boiler tubes is shown in the following table.

Controller

Type

Turbulator

Type

Load

Condition

Reduction in

Fuel Consumption

On/Off Wire Coil Full 10F

On/Off Twist Tape Full 10F

Metering Wire Coil Full 10F

Metering Twist Tape Full 10F

On/Off Wire Coil Half 10F

On/Off Twist Tape Half 10F

Metering Wire Coil Half 10F

Metering Twist Tape Half 10F

6.1

4.0

5.2

3.5

6.0

3.8

4.3

2.9

In this table the reduction value is calculated by the equation:

2
Redaction in Fael Consumption (%)

Oo - Q,

1 1 x 100

where Qq = fael consumption without tarbalator

«w

- fael consamption with, tarbalator

r( o = seasonal efficiency withoat tarbalator

= seasonal efficienty with tarbalator

It can be seen in figure 4 that for a boiler with an on/off controller, fael

utilization efficiency values decrease as the outdoor temperature rises and

that for a boiler with a metering controller fuel utilization efficiency

values first rise with the outdoor temperature and then, at temperatures above

45°F, drops with further rising in the outdoor air temperature. The latter

can be explained as follows: When the heating load is smaller than the boiler

steady-state output at its minimum firing rate, the boiler (with metering

controller) will operate in an on/off mode with 'on' being at the lowest

firing rate. In this case, the efficiency will decrease as heating load

drops. When heating load is larger than the boiler steady-state output at its

minimum firing rate, the firing rate is directly proportional to the heating

load. Since lowering of the firing rate is accompanied by increasing the gas

residence time, the boiler efficiency increases as the firing rate decreases

(as the outdoor air temperatures increases).

3
For runs with turbulators discussed in this report, their lengths are all at

3/5th of the pipe length of the last pass. Heat transfer data for the fire

tubes with the turbulators are correlated by the following equations [2]:

Nu = 0.515(Re)°- 584 (Pr) 0 - 4 (with wire coil turbulators)

Nu = 0.200(Re)0-640( Pr )0.4 (witll twisted tape turbulators)

where Nu, Re, Pr are Nusselt, Reynolds and Prandtl numbers, respectively

[3].

Calculation of the boiler seasonal performance values from the DEPAB2 output

values are listed in twelve tables which are appended to this report.

5 . CONCLUSIONS

The simulation analysis results may appear somewhat disappointing from an

improvement in energy performance viewpoint. Also, they may seem contradictory to the rather significant improvement in heat transfer performance

brought about by the insertion of the various turbulators (100-*% [2]). However, it should be realized that the majority of heat transfer occurs in the

fire box region where both radiation and convection exist and that the longer

the gases travel in the tubes, the more the heat transfer decreases due to

decreasing gas temperature. Thus, since the simulation considered that the

insertion of the turbulators was limited to only 60% of the final pass of the

fire tubes (due to practical limitations). even the potential for overall

boiler performance improvement is quite diminished.

4
On the other hand, a continual decrease in exhaust gas temperature will result

in a release of acidic condensate which must he avoided in boilers not

specifically designed to handle such a corrosive liquid. The exhaust gas

temperatures at which this condensation limitation occurs are such that it is

not theoretically possible to improve the boiler's efficiency past 88%. Relative to this boiler efficiency performance cap the wire coil turbulator (Table

2 of Appendix) appears to be improving the performance to the limit.

Although different control schemes and part load performance was considered to

a limited degree in this simulation, the effect of scale build-up due to

particulates, etc, was not considered. Therefore, the absolute values of the

performance figures listed in the appendix fables are probably greater by a

few percent than what can be expected from actual boiler performance.

6. REFERENCES

[1] Chi, I., Chera, L», and Didion, D., "A Commercial Heating Boiler

Transient Analysis Simulation Model (DEPAB2)", NBSIR 83-263 8 to U.S. Army

Facilities Engineering Support Agency, January 19 83.

[2] Junkhan, G.H., Bergles, A.E., Nirmalan, Ravigururaj an, T., "Tests of

Turbulators for Fire Tube Boilers ", Iowa State University Report to U.S.

Army Facilities Engineering Support Agency, December 1982.

[3] ASHRAE Handbook 1981 Fundamentals, Chapter 2.

5
FUEL

FIRING

RATE

FUEL

FIRING

RATE

FULL

LOAD

FIRING

RATE

FULL

LOAD

FIRING

RATE

ON/OFF CONTROLLER

220 230 240 250

STEAM TEMPERATURE, *F

METERING CONTROLLER

STEAM TEMPERATURE, *F

Figure 1. Logic for on/off controller and metering controller
HEATING

LOAD

(10®

BTU/HR)

10.0

Figure 2. Heating load curve.

Figure 3. Typical weather at Washington, D.C.

during the heating season.

7
FUEL

UTILIZATION

EFFICIENCY

FUEL

UTILIZATION

EFFICIENCY

Figure 4. Fuel utilization efficiency versus outdoor

temperature, full load at 10°F.

8
FUEL

UTILIZATION

EFFICIENCY

FUEL

UTILIZATION

EFFICIENCY

Figure 5. Fuel utilization efficiency versus outdoor

temperature, half load at 10°F.

9
SEASONAL

EFFICIENCY

SEASONAL

EFFICIENCY

Figure 6. Seasonal efficiency.

10
APPENDIX

DETAILS OF SEASONAL PERFORMANCE CALCULATIONS

ALIST OF TABLES

Table 1. Pipe Without Turbulator (Metering Controller) Full Load

at 10°F . A

Table 2. Pipe With Wire Coil (Metering Controller) Full Load at

at 10 ®F A

Table 3. Pipe With Twisted Tape (Metering Controller) Full Load at

10°F A-3

Table 4. Pipe Without Turbulator (On/Off Controller) Full Load at

10®F A

Table 5. Pipe With Wire Coil (On/Off Controller) Full Load at 10# F . . A

Table 6. Pipe With Twisted Tape (On/ Off Controller) Full Load at

10 # F . A

Table 7. Pipe Without Turbulator (Metering Controller) A-5

Table 8. Pipe With Wire Coil (Metering Controller) Half Load at 10*F . A-5

Table 9. Pipe With Twisted Tape (Metering Controller) Half Load at

10 °F A-5

Table 10. Pipe Without Turbulator (On/Off Controller) Half Load at

10 # F A-6

Table 11. Pipe With Wire Coil (On/Off Controller) Half Load at 10 # F . . A-6

Table 12. Pipe With Twisted Tape (On/Off Controller) Half Load at

10°F . A-6

A—

'MMM
BIN TEMP.

•F DAYS /BIN/YR

LOAD, 10

6 BTU

/DAY

FUEL, 10

6 BTU

/DAY LOAD, 10

6 BTU /BIN/YR

FUEL, 106 BTU

/BIN/YR

15 8.35 195.7 243.6 1634.095 2034.06

25 20.33 161.8 198.4 3289.394. 4033.472

35 46.65 127.1 153.3 5929.215 7151.445

45 43.39 91.7 108.3 3978.863 4699.137

55 26.69 55.2 66.4 1473.288 1772.216

65 15.43 18.5 25.9 285.455 399.637

TOTAL LOAD (10

6 BTU/YEAR) 16590.3

TOTAL FUEL (10

6 BTU/YEAR) 20090.0

ANNUAL EFFICIENCY (PERCENT) 82.6

Table 1. Pipe Without Turbulator (Metering Controller) Full Load at 10°F

BIN TEMP.

*F DAYS /BIN/YR

LOAD, 10 6 BTU /DAY

FUEL, 10 6 BTU

/DAY LOAD, 10

6 BTU /BIN/YR

FUEL, 106 BTU /BIN/YR

15 8.35 196.4 227.9 1639.94 1902.365

25 20.33 162.2 186.5 3727.526. 3731.545

35 46.65 127.3 145.0 5938.545 6764.25

45 43.39 92.2 104.7 4000.558 4542.933

55 26.69 55.2 64.3 1473.288 1716.167

65 15.43 18.5 24.8 285.455 382.664

TOTAL LOAD (10

6 BTU/YEAR) 16635.312

TOTAL FUEL (10

6 BTU/YEAR) 19100.524

ANNUAL EFFICIENCY (PERCENT) 87.1

Table 2 . Pipe With Wire Coil (Metering Controller) Full Load at 10°F

BIN TEMP.

°F DAYS /BIN/YR

LOAD, 10 6 BTU /DAYFUEL, 10

6 BTU

/DAY LOAD, 106 BTU /BIN/YR

FUEL, 106 BTU /BIN/YR

15 8.35 196.1 233.5 1637.435 1949.725

25 20.33 162.0 190.7 3293.46 3876.931

35 46.65 127.3 147.8 5938.545 6894.87

45 43.39 91.8 104.9 3983.202 4551.611

55 26.69 55.2 65.3 1473.288 1742.857

65 15.43 18.5 25.1 285.455 387.293

TOTAL LOAD (10

6 BTU/YEAR) 16611.385

TOTAL FUEL (10

6 BTU/YEAR) 19403.28

ANNUAL EFFICIENCY (PERCENT) 85.6

Table 3. Pipe With Twisted Tape (Metering Controller) Full Load at 10'F
BIN TEMP.

•F DAYS /BIN/YR

LOAD, 10 6 BTU

/DAY

FUEL, 106 BTU

/DAY LOAD, 10

6 BTU /BIN/YR

FUEL, 106 BTU /BIN/YR

15 8.35 199.65 251.34 1667.1 2098.7

25 20.33 163.81 207.75 3330.2 4223.5

35 46.65 127.8 164.29 5962.5 7664.1

45 43.39 91.61 120.53 3874.9 5229.9

55 26.69 55.2 75.37 1473.3 2011.7

65 15.43 18.5 28.99 285.5 447.3

TOTAL LOAD (10

6 BTU/YEAR) 16693.5

TOTAL FUEL (10

6 BTU/YEAR) 21675.2

ANNUAL EFFICIENCY (PERCENT) 77.0

Table 4. Pipe Without Turbulator (On/Off Controller) Full Load at 10°F

BIN TEMP.

•f DAYS /BIN/YR

LOAD, 10 6 BTU

/DAY

FUEL, 106 BTU

/DAY

LOAD, 106 BTU /BIN/YRFUEL, 10 6 BTU /BTN/YR

15 8.35 199.71 235.12 1667.6 1963.3

25 20.33 163.85 194.67 3331.1 . 3857.6

35 46.65 127.89 154.9 5966.2 7225.8

45 43.39 91.68 113.08 3977.9 4906.4

55 26.69 55.24 70.8 1474.2 1889.7

65 15.43 18.51 27.46 285.6 423.8

TOTAL LOAD (10

6 BTU/YEAR) 16702.6

TOTAL FUEL (10

6 BTU/YEAR) 20366.6

ANNUAL EFFICIENCY (PERCENT) 82.0

Table 5. Pipe with Wire Coil (On/Off Controller) Full Load at 10°F

BIN TEMP.

*F DAYS /BIN/YR

LOAD, 10 6 BTU /DAY

FUEL, 106 BTU

/DAY LOAD, 106 BTU /BIN/YR

FUEL, 10

6 BTU /BIN/YR

15 8.35 199.63 241.45 1666.9 2016.1

25 20.33 163.85 199.6 3331.0 . 4057.9

35 46.65 127.87 157.82 5965.2 7362.2

45 43.39 91.65 115.7 3976.7 5018.6

55 26.69 55.21 72.49 1473.6 1934.7

65 15.43 18.5 28.04 285.6 432.7

TOTAL LOAD (10

6 BTU/YEAR) 16699

TOTAL FUEL (10

6 BTU/YEAR) 20823.2

ANNUAL LI i'ICIENCY (PERCENT) 80.2

Table 6. Pipe with Twisted Tape (On/Off Controller) Full Load at 10“F

A-4
BIN TEMP.

*F DAYS /BIN/YR

LOAD, 10 6 BTU

/DAY

FUEL, 10 6 BTU

/DAY LOAD, 106 BTU /BIN/YR

FUEL, 106 BTU /BIN/YR

15 8.35 99.912 119.49 834.3 997.79

25 20.33 87.0 104.69 1768.7 . 2128.3

35 46.65 63.99 77.72 2985.13 3625.55

45 43.39 45.80 56.76 1987.11 2462.8

55 26.69 27.54 36.01 735.04 961.14

65 15.43 9.203 15.12 142.0 233.28 TOTAL LOAD (10

6 BTU/YEAR) 8452.3 TOTAL FUEL (10

6 BTU/YEAR) 10408.9 ANNUAL EFFICIENCY (PERCENT) 81 .2

Table 7. Pipe Without Turbulator (Metering Controller) Half Load at 10°F

BIN TEMP.

*F DAYS /BIN/YR

LOAD, 10 6 BTU

/DAY

FUEL, 106 BTU

/DAY LOAD, 10 6 BTU /BIN/YR

FUEL, 10 6 BTU /BIN/YR

15 8.35 100.08 113.78 835.67 950.0

25 20.33 82.19 94.16 1671.0 . 1914.4

35 46.65 64.00 74.35 2985.6 3468.56

45 43.39 45.8 54.48 1987.5 2363.94

55 26.69 27.54 34.7 735.16 926.27

65 15.43 9.203 14.74 142.0 227.5 TOTAL LOAD (10

6 BTU/YEAR) 8356.9 TOTAL FUEL (10

6 BTU/YEAR) 9850.7 ANNUAL EFFICIENCY (PERCENT) 84.8

Table 8. Pipe With Wire Coil (Metering Controller) Half Load at 10°F

BIN TEMP.

*F DAYS /BIN/YR

LOAD, 10 6 BTU

/DAY

FUEL, 10 6 BTU

/DAY LOAD, 10 6 BTU /BIN/YR

FUEL, 10 6 BTU /BIN/YR

15 8.35 100.03 115.63 835.27 965.53

25 20.33 82.23 95.61 1671.68. 1943.85

35 46.65 65.99 75.52 3078.43 3522.97

45 43.39 45.8 55.23 1987.25 2396.42

55 26.69 27.54 35.12 734.94 937.35

65 15.43 9.204 14.87 142.02 229.4 TOTAL LOAD (10

6 BTU/YEAR)

TOTAL FUEL (10

6 BTU/YEAR)

ANNUAL EFFICIENCY (PERCENT)

Table 9. Pipe With Twisted Tape (Metering Controller) Half Load at 10*F
BIN TEMP.

*F DAYS /BIN/YR

LOAD, 10 6 BTU

/DAY

FUEL, 10

6 BTU

/DAY LOAD, 106 BTU /BIN/YR

FUEL, 10

6 BTU /BIN/YR

15 8.35 99.41 131.8 830.1 1100.9

25 20.33 81.56 108.96 1658.1 . 2215.2

35 46.65 63.64 86.76 2968.6 4047.2

45 43.39 45.63 63.86 1979.7 2770.8

55 26.69 27.49 40.68 733.8 1085.7

65 15.43 9.207 17.1 142.0 263.9

TOTAL LOAD (10

6 BTU/YEAR) 8312.3

TOTAL FUEL (10

6 BTU /YEAR) 11483.7

ANNUAL EFFICIENCY (PERCENT) 72.4

Table 10. Pipe Without Turbulator (On/Off Controller) Half Load at 10°F

BIN TEMP.

*F DAYS /BIN/YR

LOAD, 10 6 BTU

/DAY FUEL, 106 BTU

/DAY LOAD, 106 BTU /BIN/YR

FUEL, 106 BTU /BIN/YR

15 8.35 99.25 123.73 828.7 1033.1

25 20.33 81.64 102.57 1659.8 . 2085.2

35 46.65 63.69 81.54 2971.4 3803.8

45 43.39 45.66 60.07 1981.1 2606.5

55 26.69 27.5 38.41 734.1 1025.3

65 15.43 9.212 16.35 142.1 252.3

TOTAL LOAD (10

6 BTU /YEAR) 8316.9

TOTAL FUEL (10

6 BTU /YEAR) 10806.2

ANNUAL EFFICIENCY (PERCENT) 77.0

Table 11. Pipe with Wire Coil (On/Off Controller) Half Load at 10°F

BIN TEMP.

*F DAYS /BIN/YR

LOAD, 10 6 BTU

/DAY

FUEL, 106 BTU

/DAY LOAD, 10 6 BTU /BIN/YR

FUEL, 10

6 BTU /BIN/YR

15 8.35 99.46 126.75 830.46 1058.4

25 20.33 81.6 104.76 1659.05 . 2129.9

35 46.65 63.66 83.42 2969.96 3891.4

45 43.39 45.63 61.45 1980.10 2666.5

55 26.69 27.5 39.28 734.01 1048.5

65 15.43 9.208 16.64 142.08 256.7

TOTAL LOAD (10

6 BTU/YEAR) 8315.7

TOTAL FUEL (10

6 BTU/YEAR) 11051.4

ANNUAL EFFICIENCY (PERCENT) 75.2

Table 12. Pipe with Twisted Tape (On/Off Controller) Half Load at 10°F

ANBS-1 14A [REv. 2-«ci U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET (Seefnswctions)

4. TITLE AND SUBTITLE

PUBLICATION or REPORT NO.

2. Performing Organ. Report No. 3. NBSIR 84-2925

Publication Date August 1984

PREDICTION OF PERFORMANCE FOR A FIRE-TUBE BOILER WITH AND WITHOUT TURBULATORS

5. AUTHOR(S)

David Didion, Lih Chera

6. PERFORMING ORGANIZATION (If joint or other than N BS, see instructions) 7. Contract/Grant No. NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE 8. Type of Report & Period Covered

WASHINGTON, D.C. 20234

9. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street, City. State, ZIP)

U.S. Array Facilities Engineering Support Agencies (USAFESA

Technology Support Division

Building 374

Fort Belvoir, Virginia 22060

10. SUPPLEMENTARY NOTES ~

_ Document describes a computer program; SF-185, FIPS Software Summary, is attached.

11. ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a si gn i fi cant

bi bliography or literature survey, mention it here)

A series of computer runs were made using DEPAB2 (the boiler simulation

computer program) . They include the runs for a fire-tube boiler "as is"

(i.e., without turbulators) , with wire-coil type turbulators , and with

twisted-tape type turbulators, respectively. Output from these runs are used to evaluate the boiler seasonal performance values under the

Washington, D.C. weather conditions. Results show that the turbulator

increases the boiler seasonal efficienty from 2.87 to 6.08%.

12. KEY WORDS (Six to twelve entries; alphabetical order; capitalize only proper names; and separate key *or<Js n \r —c: Boiler performance; boiler simulation; enhanced heat transfer; fire tube boiler-;

turbulators

13. AVAILABILITY 14. NO. OF

X Unlimited For Official Distribution. Do Not Release to NTIS

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Order From Superintendent of Documents, U.S. Government Printing Office, '•ashmgton, D.C. 20402. IS. Price

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